1. Field of the Invention
This invention relates to a method for the complete reduction of inorganic halides to obtain non-halogen inorganic substances and/or hydrides thereof and preferably also anhydrous hydrogen halides, by using reducing agents under temperature and pressure in a thermo-reducing reactor.
2. Background of the Invention
Hydrogen halides are very valuable substances in the chemical industry as they are the principal halogen source that can be used in various process. Hydrogen fluoride is a particularly important hydrogen halide. It is a colorless liquid at ambient temperature that provides the principal industrial source of fluorine and thus is the precursor to many important organic and inorganic fluorides.
Anhydrous hydrogen fluoride is known for its ability to diffuse relatively quickly through porous substances. For this reason, anhydrous hydrogen fluoride is typically used in the production of fluorinated substances, the so-called organic and inorganic fluorides. These materials are essentially refrigerants, pharmaceuticals, foam blowing agents, fire-extinguishing agents, solvents and raw materials for the production of fluorinated monomers for the plastics industry.
Other hydrogen halides such as hydrogen chloride, hydrogen bromide, hydrogen iodide, and hydrogen astatide have similar beneficial properties, albeit to a different degree, and thus there are various applications in which they can be employed.
There have been a number of processes developed in the art geared to the production of anhydrous hydrogen halides from halogenated inorganic substances. For example, anhydrous hydrogen fluoride from fluorinated inorganic substances. However, these processes are often very complex, are not fully efficient and can be very expensive and difficult to work.
An exemplary process relating to fluorinated substances is disclosed in International Publication WO99/36352 to Hage et al., which is incorporated herein by reference. This publication discloses a process to recover anhydrous hydrogen fluoride (AHF) from uranium hexafluoride. Particularly, Hage et al. disclose a multi-reaction system in which the uranium hexafluoride is reacted with a hydrogen fluoride/water azeotrope to produce uranium oxide. While ultimately Hage et al. provides a high yield of conversion, the system does not produce anhydrous hydrogen fluoride. Instead, Hage et al. obtains the anhydrous hydrogen fluoride only after a separation process to remove water. This additional separation step can be very costly and makes the process less efficient.
Another exemplary process involving fluorinated substances is one in which uranium hexafluoride is reacted to yield anhydrous hydrogen fluoride is disclosed by Yu. N. Tumanov et al. in “Mechanism of Reduction of Uranium Hexafluoride by Hydrogen,” which is incorporated herein by reference. In this article, Tumanov et al. disclose reacting uranium hexafluoride with hydrogen to produce uranium tetrafluoride and anhydrous hydrogen fluoride. While this is a more direct production of anhydrous hydrogen fluoride, Tumanov does not provide a fully efficient mechanism. Instead, Tumanov only reduces uranium hexafluoride to uranium tetrafluoride.
The mechanism of a partial reduction of uranium hexafluoride by molecular hydrogen for the dissociation equilibrium of uranium hexafluoride is similar to the Arrhenius equation. This process is typically reached at a temperature of 1800 K, where the velocity constant of reaction is in the range of 1000-4000 K.
For all practical purposes the Arrhenius equation is a sufficiently accurate representation of data as shown, for example, in FIG. 2 of Tumanov et al.
The logarithm of velocity constant of the reaction UF6→UF5+F versus the reciprocals of temperature is also expressed in Reaction Kinetics for Chemical Engineers by Stanley M. Walas, McGraw-Hill Book Company, Inc., 1959 (Fundamentals, 5. The rate equation, 6. Variables other than mass or concentration, 7. Effect of temperature and 8. Energy of activation.) at FIG. 1-2 plot log kT2 vs. 1/T, where kT2=1/sec, which document is incorporated herein by reference.
Accordingly, Tumanov provides a known mechanism for the reduction of uranium hexafluoride by hydrogen that is only a partial reduction and represents only one step of the total reduction of the uranium hexafluoride by the removal of only two fluorine atoms of the six fluorine atoms.
Thus, there is a need for an improved process in which an inorganic halide may be fully reduced to obtain a non-halogen inorganic substance and preferably anhydrous hydrogen halide. This need is equally present for all inorganic halides, but particularly important for inorganic fluoride substances.